Uses of the flexible printed wiring circuit board have been expanding since even in a limited space, steric high-density mounting is possible. In recent years, accompanied by miniaturization, weight saving, or the like, of the electronic devices, related products of the flexible printed wiring circuit board are diversified and demand of the related products are increasing. Such related products include a flexible copper-clad laminated board in which a copper foil is laminated to a polyimide film, a flexible printed wiring circuit board in which an electronic circuit is formed onto a flexible copper-clad laminated board, a flexible printed wiring circuit board attached with a reinforcing plate in which the flexible printed wiring circuit board and the reinforcing plate are laminated, a multilayered board in which flexible copper-clad laminated boards or flexible printed wiring circuit boards are laminated and bonded, and the like. When the flexible copper-clad laminated board is produced, an adhesive is generally used for adhering the polyimide film and the copper foil.
In addition, when the flexible printed wiring circuit board is produced, a film called “coverlay film” is generally used for protecting the wiring portion. The coverlay film has an insulating resin layer and an adhesive layer formed on the surface thereof. A polyimide resin composition has widely been used for forming the insulating resin layer. And the flexible printed wiring circuit board is produced by laminating the coverlay film to a surface having a wiring portion through the adhesive layer by utilizing hot press, or the like. At this time, the adhesive layer of the coverlay film is required to have firm adhesiveness to both of the wiring portion and the film base layer.
As the printed wiring board, it has been known a build-up type multilayer printed wiring board in which a conductive layer and an organic insulating layer are alternately laminated on the surface of a substrate. When such a multilayer printed wiring board is produced, the so-called “bonding sheet”, which is an insulating adhesive layer forming material, is used for bonding the conductive layer and the organic insulating layer. The insulating adhesive layer is required to have embedding property to the wiring portion and firm adhesiveness to both of the constitutional materials at the conductive portion forming the circuit (copper, etc.) and the organic insulating layer (a polyimide resin, etc.).
On the other hand, high flame retardancy is required for an adhesive to be used for producing the flexible printed wiring circuit board, and the like. In particular, flame retardancy of VTM-0 class is required in UL-94 standard. To satisfy such a high flame retardancy, a flame retardant such as a halogen-based compound, and an antimony compound has heretofore been formulated in the adhesive composition. In recent years, there has been growing an interest in environmental problems, the halogen-based compound becomes a factor which generates a harmful substance such as dioxin at the time of burning and the like after disposal, and the antimony compound is also pointed out its carcinogenicity, so that a flame-retardant adhesive not using these compounds is required.
Under these circumstances, the following technology has been known, either of which realizes adhesion to an adherend or adhesion of two parts by forming a cured product by the reaction of the contained components to each other. Patent Document 1 discloses a flame-retardant adhesive composition containing a non-halogen-based epoxy resin, a thermoplastic resin and/or a synthetic rubber, a curing agent, a curing accelerator, a phosphorus-containing plasticizer and an inorganic filler. Patent Document 2 discloses a halogen-free flame-retardant adhesive composition containing a thermoplastic resin such as a polyamide resin, a novolac type epoxy resin, a phosphor compound and melamine cyanurate. Further, Patent Document 3 discloses a flame-retardant adhesive composition containing a polyurethane polyurea resin, an epoxy resin containing no halogen element, a cyclophosphazene-based flame retardant and a flame retardant comprising a nitrogen-based compound having a melamine chemical structure.